Protective coating for glass substrate

ABSTRACT

In accordance with this invention, a chemically convertible polymeric coating composition is applied to the surface of a glass substrate and subsequently converted to a crosslinked coating by the application of heat or another form of energy. The polymeric coating composition contains at least two essential ingredients: 
     (1) a rubbery thermoplastic organic polymer; and 
     (2) an organic peroxide or hydroperoxide.

This is a continuation of application Ser. No. 558,200 filed Mar. 13, 1975, now abandoned.

BACKGROUND OF THE INVENTION

It is well-known that glass in its pristine condition is a very strong material, but that scratches and abrasion on the glass surface will considerably decrease its strength. Consequently, glass articles, for example containers such as jars, bottles, tumblers, and the like, have maximum strength immediately after formation; however, this strength diminishes when the glass article surface contacts other surfaces as may occur during the inspection, handling, packaging, shipping, and consumer use of the article.

To overcome this problem, there has been a great deal of research in the glass industry towards development of thin, tenaciously adhering, lubricic damage-preventive coatings which preserve the glass strength and allow the glass article to be handled and used by the consumer.

In the glass container industry, such damage-preventive coatings have been primarily of two types. In one type, the container is coated with a thin organic coating at the "cold end" of the annealing lehr where the temperature is in the range of 200°-400° F. These coatings have been water soluble polyoxyethylene stearate as in U.S. Pat. No. 2,813,,045 (Abbott); polyethylene as in U.S. Pat. No. 2,995,533 (Parmer and Schaefer), and U.S. Pat. No. 2,965,596 (Scharf); or other organic materials as in U.S. Pat. Nos. 3,445,275 (Bogart); 3,487,035 (Bogart); 3,357,853 (Pickard); and 3,296,174 (Pickard).

In the second type of coating, the glass container is first coated with metal oxides such as the oxides of tin, titanium, vanadium, or zirconium at the hot end of the annealing lehr where the temperature is in the range of 1000° to 1100° F. and then overcoated with a protective organic coating at the cold end of the lehr. Such dual coatings are illustrated in U.S. Pat. Nos. 3,323,889 (Carl and Steigelman); 3,425,859 (Steigelman); 3,598,632 (Long); 3,554,787 (Plymale); 3,498,825 (Wiens); 3,418,154 (Rawski); 3,420,693 (Scholes and Pickard); 3,445,269 (Bruss, et al.); 3,407,085 (Kitaj, et al.); 3,414,429 (Bruss, et al.); and 3,352,707 (Pickard). The above types of coatings are "production line" coatings because their application is accomplished as part of the forming and annealing sequence. The disclosures of these patents are incorporated herein by reference.

The success of some of these and other types of coatings, particularly those "cold end" coatings of polyethylene or polyoxyethylene stearate (with or without the "hot end" coating of TiO₂ or SnO₂) in preserving the strength of the glass containers during inspection, handling, filling, and use has permitted glass researchers to focus on the problems caused by mishandling and accidental misuse of glass containers by the consumer.

Glass containers are sometimes fractured by dropping or other accidental misuse. This problem is particularly acute when the glass container has pressurized contents such as in the case of beer or carbonated soft drinks.

In accordance with this invention, there is provided a coating for glass containers which is capable of retaining broken glass fragments upon fracture of the glass container so as to reduce the incidence of accidental injury.

Attention has been directed to this problem in the recent past. For instance, German patent disclosure No. 2,026,909, published Dec. 10, 1970, discloses coating a glass container with a loosely or firmly adhering plastic material designed to form a "bag" which retains glass fragments when the container is broken. The film is formed by fusing powdered polyethylene to the glass bottle. German patent document No. 2,149,219, published May 25, 1972, discloses coating glass containers with a film coating of a hydrolyzed ethylene-vinyl acetate copolymer. U.S. Pat. No. 3,178,049 discloses a light, composite glass container having a wall thickness of about 0.15 to 0.70 millimeters surrounded on the outside by an envelope of a thermoplastic material having a wall thickness at least equal to the glass. U.S. Pat. No. 3,415,673 discloses glass containers which are made resistant to breakage by coating the exterior surface with a thin, highly adhesive layer of plastic consisting essentially of a copolymer of ethylene and acrylic copolymers. A primer is used to tenaciously adhere the copolymer to the surface of the glass article.

Studies of the effect of organic coatings on the fragmentation of glass substrates have demonstrated that soft, flexible, "rubbery" polymeric coatings are extremely effective in retaining fragments. However, such coatings are not ordinarily suitable for use on glass containers, owing to their poor abrasion and mar resistance, low lubricity and surface tack, which preclude the handling of such coated containers on automatic filling lines. The present invention improves the physical properties and surface characteristics of such coating materials through chemical crosslinking.

DESCRIPTION OF THE INVENTION

Any suitable glass substrate is contemplated. However, in the typical practice of this invention, there is utilized a glass container. The foregoing description of embodiments and specific practices of this invention will generally be discussed in terms of a glass container substrate.

In accordance with this invention, there is prepared a coated glass substrate, having fragment-retentive properties.

More particularly, in accordance with the practice of this invention, a chemically convertible coating composition is applied to the surface of a glass substrate and subsequently converted to a protective polymer film by the application of heat or other forms of energy. The chemically convertible coating composition contains at least two ingredients:

(1) a rubbery thermoplastic organic polymer; and

(2) a peroxidic organic compound.

The term "rubbery thermoplastic organic polymer" may be defined as an eleastomeric organic polymer having an ultimate elongation of at least 100%. At the time of the application to the glass substrate, the polymer is thermoplastic, i.e. it is not crosslinked, but it can subsequently be crosslinked by the combined action of the peroxidic organic compound and heat or another form of energy.

Typical examples of suitable rubbery thermoplastic organic polymers include ethylene-vinyl acetate copolymers, hydrolyzed ethylene-vinyl acetate copolymers, ethylene-ethyl acrylate copolymers, ethylene-acrylic acid copolymers and their salts, ethylene-propylene copolymers, styrene-butadiene copolymers including both block and random copolymers, styrene-isoprene copolymers acrylonitrile-butadiene copolymers, isobutylene-isoprene copolymers, polyurethanes, thermoplastic polyesters, ethylene-propylene-diene terpolymers, styrene-ethylene-butylene block terpolymers, polypentenamers, and polyamides derived from "dimer acid".

The phrase "peroxidic organic compound" as used herein, may be defined as an organic compound which possesses at least one oxygen-oxygen bond. Typical peroxidic organic compounds include peroxides and hydroperoxides such as tert-butyl hydroperoxide, cumene hydroperoxide, diisopropylbenzene hydroperoxide, 2,5-dime thylhexane- 2,5-dihydroperoxide, p-menthane hydroperoxide 1,1,3,3-tetramethylbutyl hydroperoxide, acetyl peroxide, benzoyl peroxide, p-chlorobenzoyl peroxide, 2,4-dichlorobenzoyl peroxide, ditoluoyl peroxide, decanoyl peroxide, lauroyl peroxide, isobutyryl peroxide, diisononanoyl peroxide, pelargonyl peroxide, tert-butyl peroxyacetate, tert-butyl peroxymaleic acid, tert-butyl peroxy-isobutyrate, tert-butyl peroxypivalate, tert-butyl peroxybenzoate, tert-butyl peroxycrotonate, tert-butyl peroxy-(2-ethylhexanoate), 2,5-dimethyl-2,5-bis-(2-ethylhexanoylperoxy) hexane, 2,5-dimethyl-2,5-bis-(benzoylperoxy) hexane, 2,5-dimethyl-2,5-bis-(tert-butyl-peroxy) hexane, 2,5-dimethyl-2,5-bis-(tert-butylperoxy)-hexyne-3, di-tert-butyl diperoxyphthalate, 1,1,3,3-tetramethylbutylperoxy- 2-ethyl-hexanoate, di-tert-butyl peroxide, di-tert-amyl peroxide tert-amyl-tert-butyl peroxide, 1,1-di-tert-butylperoxy-3,3,5-trimethyl cyclohexane, bis-(tert-butylperoxy)-diisopropylbenzene, n-butyl-4,4-bis-(tert-butylperoxy)valerate, dicumyl peroxide, acetyl acetone peroxide, methyl ethyl ketone peroxide, cyclo-hexanone peroxide, tert-butylperoxy isopropyl carbonate, 2,2-bis-(tert-butylperoxy)butane, di-(2-ethylhexyl) peroxydicarbonate, and bis-(4-tert-butylcyclohexyl) peroxydicarbonate.

If desired, polymerizable ethylenically unsaturated monomers having a functionality of two or greater may also be present in the coating composition. Typical examples of such monomers include allyl acrylate, allyl methacrylate, Bisphenol A dimethacrylate, diallyl phthalate, diallyl adipate, divinyl benzene, diethylene glycol diacrylate, diethylene glycol dimethacrylate, ethylene diacrylate, ethylene dimethacrylate, hexamethylene diacrylate, methallyl acrylate, pentaerythritol tetraacrylate, pentaerthyritol triacrylate, neopentyl glycol dimethacrylate, tetraethylene glycol dimethacrylate, diallyl allylphosphonate, triallyl cyanurate, triallyl phosphate, and trimethylolpropane trimethacrylate.

Application of the coating composition to the glass substrate may be accomplished by a variety of methods known in the coating art, including spraying, dipping, roller coating, flow-coating, or silk-screening of liquid compositions containing solvents or dispersants in addition to the essential polymer and peroxidic organic compound. Also there may be used hot-melt coating, extrusion coating, powder coating, and the application of a pre-formed film or sleeve of the polymer/peroxide composition.

Following application of the coating to the substrate, the coating is dried, if necessary, to remove any volatile materials such as solvents or dispersants, and simultaneously or subsequently crosslinked by the application of heat or another form of energy, such as infrared, visible, or ultraviolet radiation; ionizing radiation; radiofrequency or microwave radiation; or ultrasonic irradiation.

In addition to the essential polymer and peroxidic material and the optional polyfunctional monomer, the protective coating composition may contain one or more additional ingredients which may modify its appearance or properties, but do not detract from its essential tendency to retain glass fragments. Such additional ingredients may include colorants, plasticizers, surfactants, reinforcing agents, foaming agents, antioxidants, ultraviolet stabilizers, antistatic agents, lubricants, flame retardents, adhesion promoters, and processing aids. Incorporation of silane adhesion promoters is particularly advantageous in those applications requiring alkali resistance, i.e. coated returnable glass containers.

In one preferred embodiment of this invention, a solution containing the rubbery thermoplastic polymer and peroxidic organic compound in a suitable volatile solvent is applied to the surface of a glass container. The coating is dried, then crosslinked by heating to the decomposition temperature of the peroxidic compound.

In a further preferred embodiment of the present invention, a peroxidic compound is incorporated into an aqueous emulsion ("latex") of a rubbery thermoplastic polymer. The resulting emulsion is applied to the surface of a glass substrate, dried at an ambient or elevated temperature, and then crosslinked by heating to the decomposition temperature of the peroxidic compound.

In a further specific embodiment of the present invention, a blowing agent such as an azo compound is incorporated into a liquid coating composition which also contains a rubbery thermoplastic polymer, a peroxidic compound, and a suitable solvent or dispersant. The resulting composition is applied to a glass surface, dried, and heated to produce a glass substrate bearing a cellular crosslinked protective coating.

The coatings of the present invention may be used in laminar combinations with other coatings, such as thin, lubricious coatings of oxidized polyethylene; primers, particularly those containing silane coupling agents, which increase adhesion to glass even in the presence of water and alkali; and abrasion-resistant exterior coatings.

The crosslinked polymeric coatings of this invention are typically of sufficient thickness (0.002 inch or greater) to resist shattering of a pressurized container, e.g. one filled with a carbonated soft drink or beer. However, thinner protective coatings of the same type may be used, particularly for applications in which the container does not contain internal pressure.

In a basic two-component system, it is contemplated that the crosslinkable polymeric compositions of this invention will contain about 90 to 99.99% by weight of the rubbery thermoplastic organic polymer and about 0.01 to 10% by weight of the peroxidic organic material.

In a basic three-component system, it is contemplated that the crosslinkable polymeric compositions of the present invention will ordinarily contain about 70 to 99.99% by weight of the rubbery thermoplastic organic polymer, about 0.01 to 10% by weight of the peroxidic organic material, and about 0 to 30% of the optional polyfunctional monomer.

The proportions of such additional ingredients as may be present in the two or three component system are not considered in calculating these percentages. 

We claim:
 1. A process for forming a protective film on the surface of a glass container which comprises;applying a polymeric crosslinkable coating composition to the glass substrate container, the coating composition consisting of 90 to 99.99% by weight of a rubbery thermoplastic organic polymer and 10 to 0.01% by weight of a peroxidic organic compound, said polymer being an elastomeric organic polymer having an ultimate elongation of at least 100% and being crosslinkable, and said peroxidic organic compound possessing at least one oxygen-oxygen bond, and energizing the polymeric composition in situ on the container surface so as to crosslink the composition and form a protective polymeric film having a thickness of at least 0.002 inch.
 2. The process of claim 1 wherein said rubbery thermoplastic organic polymer is selected from the group consisting of ehtylene-vinyl acetate copolymers, hydrolyzed ethylene-vinyl acetate copolymers, ethylene-ethyl acrylate copolymers, ethylene-acrylic acid copolymers, ethylene-propylene copolymers, styrene-butadiene copolymers, styrene-isoprene copolymers, acrylonitrile-butadiene copolymers, isobutylene-isoprene copolymers, polyurethanes, thermoplastic polyesters, ethylene-propylene-diene terpolymers, styrene-ethylene-butylene block terpolymers, polypentenamers, and polyamides derived from a dimer acid.
 3. The process of claim 2 wherein said peroxidic organic compound is selected from the group consisting of tert-butyl hydroperoxide, cumene hydroperoxide, diisopropylbenzene hydroperoxide, 2,5-dimethylhexane-2,5-dihydroperoxide, p-menthane hydroperoxide; 1,1,3,3-tetramethylbutyl hydroperoxide, acetyl peroxide, benzoyl peroxide, p-chlorobenzoyl peroxide, 2,4-dichlorobenzoyl peroxide, ditoluoyl peroxide, decanoyl peroxide, lauroyl peroxide, isobutyryl peroxide, diisononanoyl peroxide, pelargonyl peroxide, tert-butyl peroxyacetate, tert-butyl peroxymaleic acid, tert-butyl peroxy-isobutyrate, tert-butyl peroxypivalate, tert-butyl peroxybenzoate, tert-butyl peroxycrotonate, tert-butyl peroxy-(2-ethylhexanoate), 2,5-dimethyl-2,5-bis-(2-ethylhexanoylperoxy) hexane, 2,5-dimethyl-2,5-bis-(benzoylperoxy) hexane, 2,5-dimethyl-2,5-bis-(tert-butyl-peroxy) hexane, 2,5-dimethyl-2,5-bis-(tert-butylperoxy)-hexyne-3,di-tert-butyl diperoxyphthalate, 1,1,3,3-tetramethylbutylperoxy-2-ethyl-hexanoate, di-tert-butyl peroxide, di-tert-amyl peroxide, tert-amyl-tert-butyl peroxide, 1,1-di-tert-butylperoxy-3,3,5-trimethyl cyclohexane, bis-(tert-butylperoxy)-diisopropylbenzene, n-butyl-4,4-bis-(tert-butylperoxy)valerate, dicumyl peroxide, acetyl acetone peroxide, methyl ethyl ketone peroxide, cyclo-hexanone peroxide, tert-butylperoxy isopropyl carbonate, 2,2-bis-(tert-butylperoxy)butane, di-(2-ethylhexyl) peroxydicarbonate, and bis-(4-tert-butylcyclohexyl) peroxydicarbonate.
 4. A process for forming a protective film on the surface of a glass container which comprises;applying a polymeric crosslinkable coating composition to the glass container surface, the coating composition comprising 70 to 99.99% by weight of a rubbery thermoplastic organic polymer, up to 30% by weight of a polymerizable ethylenically unsaturated monomer and 0.01 to 10% by weight of a peroxidic organic compound, said polymer being an elastomeric organic polymer having an ultimate elongation of at least 100%, being crosslinkable, and being selected from the group consisting of ethylene-vinyl acetate copolymers, hydrolyzed ethylene-vinyl acetate copolymers, ethylene-ethyl acrylate copolymers, ethylene-acrylic acid copolymers, ethylene-propylene copolymers, styrene-butadiene copolymers, styrene-isoprene copolymers, acrylonitrile-butadiene copolymers, isobutylene-isoprene copolymers, polyurethanes, thermoplastic polyesters, ethylene-propylene-diene terpolymers, styrene-ethylene-butylene block terpolymers, polypentenamers, and polyamides derived from a dimer acid, said polymerizable ethylenically unsaturated monomer having a functionality of at least two and being selected from the group consisting of allyl acrylate, allyl methacrylate, Bisphenol A dimethacrylate, diallyl phthalate, diallyl adipate, divinyl benzene, diethylene glycol diacrylate, diethylene glycol dimethacrylate, ethylene diacrylate, ethylene dimethacrylate, hexamethylene diacrylate, methallyl acrylate, pentaerythritol tetraacrylate, pentaerythritol triacrylate, neopentyl glycol dimethyacrylate, tetraethylene glycol dimethacrylate, diallyl allylphosphonate, triallyl cyanurate, triallyl phosphate, and trimethylolpropane trimethacrylate, and said peroxidic organic compound possessing at least one oxygen-oxygen bond, and energizing the polymeric composition in situ on the container surface so as to crosslink the composition and form a protective polymeric film having a thickness of at least 0.002 inch.
 5. The process of claim 4 wherein said peroxidic organic compound is selected from the group consisting of tert-butyl hydroperoxide, cumene hydroperoxide, diisopropylbenzene hydroperoxide, 2,5-dimethylhexane-2,5-dihydroperoxide p-menthane hydroperoxide; 1,1,3,3-tetramethylbutyl hydroperoxide, acetyl peroxide, benzoyl peroxide, p-chlorobenzoyl peroxide, 2,4-dichlorobenzoyl peroxide, ditoluoyl peroxide, decanoyl peroxide, lauroyl peroxide, isobutyryl peroxide, diisononanoyl peroxide, pelargonyl peroxide, tert-butyl peroxyacetate, tert-butyl peroxymaleic acid, tert-butyl peroxy-isobutyrate, tert-butyl peroxypivalate, tert-butyl peroxybenzoate, tert-butyl peroxycrotonate, tert-butyl peroxy-(2-ethylhexanoate), 2,5-dimethyl-2,5-bis-(2-ethylhexanoylperoxy) hexane, 2,5-dimethyl-2,5-bis-(benzoylperoxy) hexane, 2,5-dimethyl-2,5-bis-(tert-butyl-peroxy) hexane, 2,5-dimethyl-2,5-bis-(tert-butylperoxy)-hexyne-3, di-tert-butyl diperoxyphthalate, 1,1,3,3-tetramethylbutylperoxy-2-ethyl-hexanoate, di-tert-butyl peroxide, di-tert-amyl peroxide, tert-amyl-tert-butyl peroxide, 1,1-di-tert-butylperoxy-3,3,5-trimethyl cyclohexane, bis-(tert-butylperoxy)-diisopropylbenzene, n-butyl-4,4-bis-(tert-butylperoxy)valerate, dicumyl peroxide, acetyl acetone peroxide, methyl ethyl ketone peroxide, cyclo-hexanone peroxide, tert-butylperoxy isopropyl carbonate, 2,2-bis-(tert-butylperoxy)butane, di-(2-ethylhexyl) peroxydicarbonate, and bis-(4-tert-butylcyclohexyl) peroxydicarbonate. 